#!/usr/bin/env perl

use strict;
use warnings;

{
    local $/ = "\n>";

    while (<DATA>) {
        $_ = substr $_, 1 if $. == 1;

        my ($head, $data) = split /\n/;

        if ($head eq $ARGV[0]) {
            print "Found! Head: '$head'; Data: '$data'\n";
            last;
        }
    }
}

__DATA__
>head1
data1
>head2
data2
>head3
data3

##</code><code>##

$ pm_1159403_fasta.pl head1
Found! Head: 'head1'; Data: 'data1'
$ pm_1159403_fasta.pl head2
Found! Head: 'head2'; Data: 'data2'
$ pm_1159403_fasta.pl head3
Found! Head: 'head3'; Data: 'data3'